Method of electroplating copper-lead alloy



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739 METHOD OF ELECTROPLATING COPPER-LEAD ALLOY Wilbur" G. Hespenheide and Charles L. Faust, Columbus, Ohio, assiguors',flby mesne assignments, to American Brake Shoe Company, New York, N. Y., a corporatioh of Delaware I No Drawing. Application June 25, 1952, Serial No. 295,543

8 Claims. (Cl. 204-23) This invention relates to electrodeposited copper-lead alloys and methods for the electrodeposition thereof. In particular, it relates to electrodepositing liners of copperlead'alloys on bearing shells of steel or other metal.

.It'is well known in the metallurgical field that copperlead bearing liners have superior properties for use in heavy-duty service for industrial engines and machinery. According toIpresent-day' practice in this field, copperlead alloys are first' prepared bymelting copper and lead together and are .thencast in molten form onto the inside surfaceof cylinder of steel or other metal. The copperlead alloy mayalso be cast onto a flat strip, of the proper thickness, whichis subsequently cut to the desired lengths and formed into bearing half-shells.

Due to the fact, that the lead and copper are, for all practical purposes, insoluble in' each other in the solid and liquid state, the copper-lead alloy, bearing liners formed by these methods consist of alace work or dendritic structure 0t copper, surrounded by metallic lead. Thus, during solification of a mechanical mixture of copper and lead, the copper crystallizes in a dendritic structure, and the lead then solidifies in the region between these dentrites. vSuch separation between'the two constituents might be advantageous, since the lead phase has a lubricating property which is highly desirable in bearing performance. However, the segregation of lead also causes a serious disadvantage, since there is a pronounced tendencyifor the lead to separate out in a continuous layer at the interface between the metal backing element andthe copper-lead alloy bearing layer. This interfacial layer of lead presents a zone of mechanical weakness, and consequently the performance of the bearing is not as satisfactory as it would be if such lead zone were not pr'esentbetween the. metal backing member and the copper-lead alloy bearing liner. I

Of course, enhancementof bearing. performance is directly related to the extent and uniformitywith which lead is dispersed in the copper matrix. Thus, inherent lubrieating efiects are increasednoise is eliminated to a greater extent, and thebearing iseasier to machine. Prior attempts to prepare suitable copper-lead bearings by casting methqds in whichthere isr asatisfactory quantity, dispersion, concentration,anddistribution of lead in copper havebeenretarded and made.ditiicult by, among other things, vditferences in the meltingpoint of copper and lead; separation of lead upon cooling rather than on alloying thereofwith copper; and the difference in specific gravity between the two metals. 7 p h For. many years the bearing industry has sought ways to produce a copper-lead alloy bearing liner without the inherent disadvantages that result from preparing the alloy by melting and casting techniques. One of the methods proposed has been thesimultaneous,electrodeposition of copper and lead. Numerous suggestions have been madefor electrodepositing copper-lead alloys, but

none has produced an alloy plate having the proper com- I position and, at the same time, possessing the required physical properties for a bearing liner.

The prior-art copper-lead alloy plating developments have produced copper-lead electrodeposits that were either extremely brittle or wholly unsuitable for bearing liners due to the fact that the codeposited copper and lead were noncoherent and appeared as a powdery spongelike metal. Further, the codeposits of copper and lead reported in the technical literature are extremely hard, not being amenable to customary metallurgical heat treatments, and have, therefore, resisted annealing to the lesser hardness which is desirable for bearing metal.

It has been proposed, as" a specific example, to codeposit copper and lead from a bath containing copper hydroxide and lead acetate] This deposit, however, is characterized by many hairline cracks forming an irregular network extending from'the surfaceof the deposit to the face of the backing'metal. Further, the deposit islamimat in form, layers of' lead occurring between adjacent copper layers and"..a1'so there is'an irregular dispersion of lead in the .copperfmatrix, As a consequence, the deposit is brittle and incapable of practical use, and'in anattempt to properly and satisfactorily relate the copper and lead phases, a special annealing technique is employed. However, a satisfactory, softness can be attained only by annealing at temperatures above the meltingpoint oflead for a prolonged period. This heat treatment causes the lead to sweat out forming an interfacial layer of lead as in casting techniques and also large aggregations of lead ,on the surface of the deposit. In addition, grosscopper recrystallization grains are produced, and it will be seen that while the desired softness is attained, a much weakened structure is produced. This prior method for producing copper-lead bearing linings by co-depositionon a suitable backing ,is typical of what has heretofore been accomplished in the art; 7,

It is well known. in the art of, alloy plating that there is no obvious equivalency between the methods. for electrodepositing one. or more pure metals directly and methods for electrode'positingalloys of these metals. In other words, the nature of the art is such that there is .no suggestion or previs'ioniwhich ,makes itpossible vto take a satisfactory electrodeposition bath-for copper on one hand an for lead on the other, mix them together, and thus obtain a suitablecopper-lead alloy plating solution which will' thereby give an alloy having predetermined properties selected for a given usage.

There are, of course,'known methods of alloy plating by which alloys'o'f two or more metals can be formed. These are especially useful when other methods, such as melting and casting, are unsuccessful. Again, however, that same knowledge does not teach the procedure by which known plating methods can be combined to imr'nediately produce thedesired results; All this is clearly shown by the'knowri methods of electrodepositing copper and lead asptire'metal's. For example, copper can be deposited in good formi for ma uses from a, copper flluoborate solution. Yet, when copper fluob'orat'e' and lead fiuobor'ate a'reiii the same solution,'either a powde y, i y ei bf fil a pper. or j ie y hard, extremely brittle codeposit of' copper and lead is obtained, when alloys comprisingf over 25 per cent copper are sought. Neither of these codeposits is'suitable for a bearing metal. 7

Likewise, it is known that copper can be deposited from a cyanide solution whichcontains'fr'ee alkali as well as freecy anideli Lead has'beendeposited from a' solution of lead oxide iiiah' alkaline'tartrate solution. Ye'twh'en the alkaline cyanide-copper solution and the alkaline tartrate-lead solution are mixed; the" resulting" solution will not produce the satisfactory codeposition of copper and lead which is required for bearings.

A desirable and usable copper-lead alloy deposit might be expected if the teachings of alloy plating were directly transferable from one pair of metals to another. The technical literature shows that an alkaline silver cyanidelead tartrate solution can electrodeposit a very satisfactory bearing alloy of high-silver and low-lead composition. Yet attempts to electrodeposit a suitable .highcopper low-lead alloy from a comparable solution is totally without success.

It is recognized that codeposits of copper and lead can be obtained in a dense metallic form. However, this type of alloy is too brittle and too hard to be used as a bearing material. Furthermore, the alloy cannot be softened by customary heat treatments to produce a product having a suitable ductility and hardness.

In accordance with the present invention, it has now been found that suitable copper-lead alloys can be electrodeposited, and it has also been discovered that by heattreating such alloys the same can be softened for use as a bearing material on a steel or equivalent backing member. Further, by the same technique, to be described hereinafter, the copper-lead alloy plate can be electrodeposited on other bearing backing materials to produce a bearingalloy liner.

The present process is based on a combination of copper and lead salts which has not heretofore been known or ever shown to be useful in electrodepositin g alloys. For example, we have found that a combination of coppercyanide and lead pyrophosphate produces a stable solution in water, and that this solution will give copper-lead alloy codeposits which can be subsequently heat-treated to produce satisfactory bearing liners.

It is, therefore, an object of this invention to electrodeposit copper-lead alloys by a novel process.

It is another object of this invention to effectively electrodeposit copper-lead alloys on a metal backing material and subsequently treat the alloys to provide a satisfactory bearing.

It is a further object of this invention to avoid in copperalloy electrodeposits having a metastable solid solution of lead in copper harmful segregations of lead that render such deposits detrimental for use as a satisfactory bearing material.

Yet another object of this invention is to produce highcopper, low-lead alloy electroplates.

Further objects should be apparent from what has hereinbefore been discussed and outlined, and other objects are also embodied in the description to follow as will be appreciated by those who are skilled in the art.

Desired alloy compositions for most general bearing use are in the range of from to 20% lead, balance copper. It has been found, in accordance with the present invention, that copper-lead alloys containing from 5 to 95% lead can be electrodeposited from cyanide-pyrophosphate baths, and that these baths are stable during long periods of continuous use. The desired high-copper, lowlead alloys are obtained in a form which can be suitably heat-treated, as will hereinafter be described.

The alloy electroplates in this composition range are, according to X-ray examination, solid solutions of lead in copper, since X-ray analysis in the present instance shows only a copper phase with a strained lattice. This solid solution is totally unpredicted by the usual thermal diagrams of copper-lead alloys, since the solubility of lead in copper certainly lies well below yet it is the result of the infinitely fine process of atom-by-atom codeposition of copper and lead. The resulting solid solution is very stable during ordinary low-temperature heat treatment, and in view of the fact that this absolute condition of solubility is, thermally speaking, not a normal one, such solutions occurring as the result of present practice will be referred to as metastable.

The plating bath for the copper-lead alloy electrodeposition comprises a water solution containing coppercyanide and lead-pyrophosphate complexes. Lead pyrophosphate is the only known inorganic salt of lead which is appreciably soluble in the pH range of 6 to 10. Since lead forms no cyanide complex, it is necessary to have lead in a complex with so little ionization that there are substantially as few free lead ions in the solution as there are copper ions in the solution of copper-cyanide. Leadpyrophosphate forms such a complex, and thus has been found to be highly desirable for codepositing copper and lead in an alloy form that is suitable for bearing performance. Since suppressed copper forms no pyrophosphate complex when cyanide is present, an excellent copper-lead alloy electrodepositing bath is formed by having coppercyanide and lead pyrophosphate complexes present in the same solution.

The lead pyrophosphate complex is formed by addition to water of an alkali pyrophosphate salt and a soluble lead salt which will ionize to form plumbous lead. Copper cyanide is added to the bath, and an additional amount of an aikali metal cyanide is added to suppress the copper. it may also be desirable to add an alkali metal dihydrogen orthophosphate for the purpose of buffering against changes in pH.

The amount of the bath components are dependent on the composition of alloy desired, and pH of the solution, and other factors. In general, an increase in the alkali metal cyanide concentration will result in a decrease in the copper content of the plate. As has been heretofore stated, the pH of the bath must be maintained within the range of about 6 to 10, in order to keep the lead pyrophosphate from precipitating out of solution. The temperature of the bath during electrodeposition should range from about to F. An increase in bath temperature will result in an increase in the copper content of the alloy deposited.

In the electrodeposition of the alloy the metal surface to be coated is made the cathode, the anodes preferably being made from an alloy having approximately the same composition as that desired in the bearing liners. It is also possible to use pure copper anodes, and in this case periodic additions of suitable salts are necessary to maintain the desired concentration of lead in the bath. As an alternative arrangement, there may be provided individual anodes of lead and copper using a dual anode circuit. The areas of these latter anodes and the current supplied to each of them should be adjusted to maintain the desired rate of dissolution of the metals, thus to replenish the metals plated from the bath.

The anodes can be stationary, suitably disposed about the axis of a cylindrical assembly, and agitation can be provided by continuously rotating, in one direction, paddles suspended from a disc between the anode and the surface of the bearing shell, which is immersed in the plating bath. Alternatively, the anodes can be suspended inside of the bearing shell and arranged to rotate. In the latter arrangement, it may be desirable to cyclically reverse the direction of rotation of the anodes to provide a mixing-agitation of the solution at the surface of the bearing shell. As a result, fresh solution is supplied to the anode and cathode surfaces during deposition, facilitating control of the physical properties of the plate. Suitable agitation may also be provided by moving the cathode if desired.

Although it is not necessary to provide a diaphragm or anode bags, their use is preferred. Very satisfactory coatings haveresulted from enclosing the anodes in bags. When used with rotating anodes, the bags may be suspended so as to rotate with the anodes. For simpler control of the process, it is preferred to use a diaphragm having a cylindrical shape surrounding the anodes. When rotating paddles are used as agitators, they should be separated from the anodes by the diaphragm. The diaphragm serves to contain any particles which may drop from the anodes, and prevents attachment of the particles to the plated surface with a resulting surface roughness.

Continuous filtration is also desirable and may be accomplished by withdrawing solution from the anode compartment and returning it to the cathode compartment. A filter press can be inserted in the line used for circulating the solution. This press may, or may not, use activated carbon for purification.

The current density will, of course, vary with the composition of the bath, temperature, agitation, etc. However, satisfactory coatings have been deposited with currents varying from to 40 amp. per sq. ft. A periodic current reversal has been found to be beneficial in securing sound deposits, although its use is not essential in this process. The use of such a current tend to eliminate pitting and reduce the amount of roughness and columnar structure. However, the reverse current may also tend to cause brittleness and cracking of the plate.

It is preferable that the steel or other metal surfaces be given a copper strike plate by any of the conventional plating methods, such as a copper cyanide solution. The usual techniques of vapor degressing, alkaline cleaning, dipping in hydrochloric acid, etc., are used to prepare the surface for the alloy coating. Where small dimensional tolerances are desired, the metal shells can be copper plated and then machined to the proper inside diameter. In such cases a thinner copper-lead alloy plate is desirable as compared to the alloy plate deposited over a copper strike plate. The bearing shell can then be made anodic in the copper-lead alloy plating bath, as a final cleaning operation, before being coated with the alloy.

The following examples will serve to illustrate the invention with greater particularity:

Example I An alloy having a composition of 40 per cent copper and 60 per cent lead was deposited on a steel cathode from the following aqueous bath:

G./l. Potassium pyrophosphate (KrPzOmBHzO) 100 Potassium cyanide 34 Copper cyanide 22.5 Plumbous chloride 2.7

The bath was maintained at 165 F. and operated at a pH of about 8.5. The pH adjustments were made by adding potassium hydroxide (KOH) or hydrochloric acid (HCl). Cast alloy anodes of a composition approximately the same as the alloy coating were used. The current density was 30 amp./ sq. ft.

Example 11 The following aqueous bath was used to form an alloy plating of 40 per cent copper and 60 per cent lead:

G./l. Potassium pyrophosphate 100 Potassium cyanide 40 Copper cyanide 22.5 Plumbous chloride 3 Potassium dihydrogen orthophosphate The bath was maintained at a temperature of 130 F., and at a pH value of 8.5. The current density was 10 amp./ sq. ft. and the anode and cathode arrangement was similar to that of Example I.

Example III An alloy having a composition of 75 per cent copper and per cent lead was deposited by increasing the bath of Example II to a temperature of 170 F.

Example IV The following aqueous bath was used to deposit an alloy composed of 80 per cent copper and 20 per cent lead:

G./l. Potassium pyrophosphate 120 Potassium cyanide 50 Copper cyanide 28 Plumbous chloride 3.5 Potassium dihydrogen orthophosphate 20 The bath temperature was F., and the pH was maintained at about 8.0.

After the copper-lead alloy has been deposited, it is necessary that it be annealed in order to reduce the hardness to a value suitable for bearings. Annealing at temperatures less than 800 F., commonly used for low melting alloys, does not result in sufiicient ductility, and causes the formation of two phases from the metastable solid solution of lead and copper. Thus, before the desired softening can be accomplished, lead is sweated out of the alloy and appears on the surface of the bearing and the interface between the alloy and the basis material as globules of pure lead or lead containing a small amount of copper. This physical structure is highly undesirable and detrimental to the performance of the bearing as was noted hereinbefore.

In accordance with thepresent procedure, exposure to temperatures of about 1000 F. for short period of time in a non-oxidizing atmosphere will soften and anneal the copper-lead alloy plates to a hardness value that is suitable for hearing metals. Induction heating could accomplish this result, but the annealing of large bearing shells having a thin liner would require large and expensive induction heating equipment. Very satisfactory results have been obtained with these alloys by immersion thereof in a fused salt bath, the procedure being the same as disclosed in copending application Serial No. 295,542, filed June 25, 1952.

Although the preceding description of the novel copperlead alloy, coating and the process for depositing it have been described for use in bearing liners, the alloy can be electrodeposited by other techniques and equipment commonly used in the plating industry. For example, a satisfactory copper-lead coating can be formed on a fiat panel which is suspended from a moving work bar oscillating back and forth in the plating solution. The plate can also be deposited in a closed circuit in which the solution is circulated by pumps and flowing at a suitable rate in a tube or pipe. The tube or pipe is then coated with the alloy electroplate.

From the foregoing it will be seen that by the present invention copper-lead electrodeposits may be obtained in satisfactory form, and, particularly in the case of bearing linings, such deposits may be suitably obtained in the form of high-copper, low-lead alloys. There has also been disclosed a subsequent annealing process by which the hardness of the alloy plate may be reduced without segregation of the lead in the alloy and without formationof-any lead interface layer between the alloy coating and the base material.

Thus, while we have illustrated and described the preferred embodiments of our invention, it is to be understood that these are capable of variation and modification, and we therefore do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes and alterations as fall within the purview of the following claims.

We claim:

1. A method of electrodepositing on an article arranged as a cathode a copper-lead alloy including the step of passing an electric current through an aqueous bath containing, as the essential ingredients for co-depositing copper and lead on said article, copper cyanide in a concentration of about 22.5 to 28 grams per liter as the source of copper for the alloy, free cyanide to suppress copper ionization, and lead pyrophosphate as the source of lead for the alloy, said lead pyrophosphate being derived from a soluble lead salt in a concentration of about 2.7 to 3.5 grams per liter and alkali metal pyrophosphate salt in a concentration of about 100 to 120 grams per liter,

said bath having a pH of about 8 to maintain lead pyrophosphate in solution. a r

2. An electrodepositing bath for co-depositing copper and lead as an alloy comprising, as the essential ingredicuts for co-depositing copper and lead, copper cyanide in a concentration of about 22.5 to 28 grams per liter as the source of copper for the alloy, free cyanide to suppress copper ionization, and lead pyrophosphate as the source of lead for the alloy, said lead pyrophosphate being derived from a soluble lead salt in a concentration of about 2.7 to 3.5 grams per liter and alkali metal pyrophosphate salt in a concentration of about 100 to 120 grams per liter, said bath having a pH of about 8 to maintain lead pyrophosphate in solution.

3. A method of electrodepositing copper-lead alloys containing from about to about 95 per cent lead on an article arranged as a cathode, including the step of passing an electric current through an aqueous bath containing,

as the essential ingredients for co-depositing copper and lead on said article, copper cyanide as the source of cop per for the alloy, free cyanide to suppress copper ionization, and lead pyrophosphate as the source of lead for the alloy, said lead pyrophosphate being derived from a soluble lead salt and an alkali metal pyrophosphate salt,

and said bath having a pH of about 8 to maintain lead pyrophosphate in solution.

4. An electrodepositing bath, containing as the essential ingredients for co-depositing copper and lead as an alloy, copper cyanide as the source of copper for the alloy, free cyanide to suppress copper ionization, and lead pyrophosphate as the source of lead for the alloy, said lead pyrophosphate beingderived from a soluble lead salt and alkali metal pyrophosphate, and said bath having a pH of about 8 to maintain lead pyrophosphate in solution.

5. A method of producing a bearing shell lined with a copper-lead bearing alloy comprising the steps of disposing the shell as a cathode to be plated in an aqueous electroplating bath containing as the essential ingredients for co-depositing copper and lead, copper cyanide as the source of copper for the alloy, free cyanide to suppress copper ionization, and lead pyrophosphate derived from a soluble lead salt and alkali metal pyrophosphate as the source of lead for the alloy, said bath having a pH of about 8 to maintain lead pyrophosphate in solution, and after the deposit has been obtained rapidly annealing the lining at a temperature about 800 F. to reduce the lining to hearing softness.

6. A method of producing a bearing shell electrolytically lined with a copper-lead bearing alloy comprising the steps of disposing the shell as a cathode to be plated in an aqueous electroplating bath containing copper cyanide in a concentration of about 22.5 to 28 grams per liter as the source of copper for the alloy, alkali metal cyanide in a concentration of about 34 to about grams per liter to provide free cyanide to control copper ionization, and lead pyrophosphateas the source of lead for the alloy, said lead pyrophosphate being derived from a soluble lead salt in a concentration of about 2.7 to 3.5 grams per liter and alkali metal pyrophosphate in a concentration of about to'120 grams per liter, said bath having a pH of about 8 to maintain lead pyrophosphate in solution, and after the deposit has been obtained rapidly annealing the lining at a temperature of about 800 F. to reduce the lining to hearing softness.

7. A method of electrodepositing copper-lead alloys on an article to be plated arranged as a cathode including the step of passing an electric current through an aqueous bath containing copper cyanide in a concentration of about22.5 to 28 grams per liter as the source of copper for the alloy, alkali metal cyanide in a concentration of about 34 to 50 grams per liter to provide free cyanide to control copper ionization, and lead pyrophosphate as the source of lead for the alloy, said lead pyrophosphate being derived from a soluble lead salt in a concentration of about 2.7 to 3.5 grams per liter and alkali metal pyrophosphate in a concentration of about 100 to grams per liter, said bath having a pH of about 8 to maintain lead pyrophosphate in solution. 7

8. An aqueous electrodepositing bath for depositing a copper-lead alloy on an article to be plated arranged as a cathode and containing copper cyanide in a concentration of about 22.5 to 28 grams per liter as the source of copper for the alloy, alkali metal cyanide in a concentration of about 34 to 50 grams per liter to provide free cyanide to control copper ionization, and lead pyrophosphate as the source of lead for the alloy, said lead pyrophosphate being derived from a soluble lead salt in a concentration of about 2.7 to 3.5 grams per liter and alkali metal pyrophosphate in a concentration of about 100 to 120 grams per liter,,said bath having a pH of about 8 to maintain lead pyrophosphate in solution.

References Cited in the file of this patent UNITED STATES PATENTS 923,864 Levy June 8, 1909 1,397,514 Haines et a1. Nov. 22, 1921 V FOREIGN PATENTS 361,892 France Nov. 7, 1906 1,657 Great Britain of 1897 10,133 Great Britain of 1915 OTHER REFERENCES Monthly Review, American Electroplaters Society, vol. 33, 1946, pages 18-23 and 88.

Trans. Electrochemical Society, vol. 73, 1938, pages 384 and 406.

Treatise on Chemistry, vol. II, 1913, page 899.

Trans. Electrochemical Society, vol, 73, 1938, pages 384-394, 405 and 406. 

1. A METHOD OF ELECTRODEPOSITING ON AN ARTICLE ARRANGED AS A CATHODE A COPPER-LEAD ALLOY INCLUDING THE STEP OF PASSING AN ELECTRIC CURRENT THROUGH AN AQUEOUS BATH CONTAINING, AS THE ESSENTIAL INGREDIENTS FOR CO-DEPOSITING COPPER AND LEAD ON SAID ARTICLE, COPPER CYANIDE IN A CONCENTRATION OF ABOUT 22.5 TO 28 GRAMS PER LITER AS THE SOURCE OF COPPER FOR THE ALLOY, FREE CYANIDE TO SUPPRESS COPPER IONIZATION, AND LEAD PYROPHOSPHATE AS THE SOURCE OF LEAD FOR THE ALLOY, SAID LEAD PRYOPHOSPHATE BEING DERIVED FROM A SOLUBLE LEAD SALT IN A CONCENTRATION OF ABOUT 2.7 TO 3.5 GRAMS PER LITER AND ALKALI METAL PYROPHOSPHATE SALT IN A CONCENTRATION OF ABOUT 100 TO 120 GRAMS PER LITER, SAID BATH HAVING A PH OF ABOUT 8 TO MAINTAIN LEAD PYROPHOSPHATE IN SOLUTION. 